Pneumonia in children with juvenile idiopathic arthritis in Finland 1999-2014: a nationwide retrospective register linkage study.

Objectives: To compare the incidence of pneumonia in children with juvenile idiopathic arthritis (JIA) to the aged-matched general population and to evaluate the use of anti-rheumatic medication among children with JIA and pneumonia.

Methods: The National Hospital Discharge Register collects data on ICD-diagnoses of hospital patients in Finland. From this register, patients with JIA under 18 years of age with pneumonia from 1999 through 2014 were identified. The control group consisted of age-matched patients derived from the general population with a diagnosis of pneumonia made in the same calendar year as the pneumonia of the JIA patients. The patient records of the children with JIA were scrutinised for the use of anti-rheumatic medication.

Results: We identified 223 pneumonias among the JIA patients (56,161 patient-years) and 53,058 pneumonias in the control group (17,546,609 person-years). The incidence of pneumonia in children with JIA was 386 (annual range 131-639) and in the control group 303 (annual range 225-438) per 100,000 person-years. The incidence of pneumonia increased significantly over time among JIA patients (p=0.013) and in the control group (p<0.001). Through 2007-2014 the rate of pneumonia was significantly higher among children with JIA (p<0.001) than control children. We found 150 JIA patients with pneumonia confirmed by positive chest radiograph. Altogether 47% of the JIA patients had combination medication. The use of methotrexate and biologic agents increased significantly over time (p=0.016 and p<0.001, respectively).

Conclusions: The incidence of pneumonia increased in children with JIA and in the general population from 1999 to 2014. During 2007-2014 JIA patients had a significantly higher rate of pneumonia than age-matched controls. The use of active anti-rheumatic medication was common.